on Ionization produced by Hot Platinum in Gases. 409 
that the curve after exposure furnishes two maxima before 
arriving at the final rise which represents the original leak. 
The curve with points thus: © represents the rate of decay 
of the current at the various temperatures; as has been 
pointed out already, the curve for the rate of decay closely 
imitates that for the current itself. 
Ney 
Fig. oe 
) 
a 
LRT Ny 
1:76 X10~/ amp 
CURRENT [/ 
200 500 400 500 600 700 800 
Experiments similar to that whose results are shown in 
fig. 6 were carried out under various. conditions. All the 
curves showed at least one well-marked maximum whose 
position lay between 430° and 520° C. Most of the curves 
obtained with the discharge in oxygen and all of those with 
air gave a second maximum whose position varied between 
600° and 693° C.; with nitrogen the second hump was not 
so well marked. The position of these maxima naturally 
depends on the length of time the testing wire is maintained 
at the various temperatures; in all these experiments the 
time in question was four minutes. 0 
In the case of oxygen, experiments were made with pres- 
sures in the discharge-tube ranging from °416 to ‘02 mm. 
At the low pressures the discharge was produced by an in- 
duction-coil, and the walls of the tube were bright yellow 
with the phosphorescence due to cathode rays. The variation 
in the maxima seemed to depend on some obscure change in 
the cathode, or in the discharge, rather than on the pressure 
or nature of the gas, although this point requires further 
investigation. Hxperiments made with aluminium cathodes 
